(a) Field of the Invention
The present invention relates to a slip control method for a traction control system (TCS) used in vehicles.
(b) Description of the Related Art
A TCS is provided in some vehicles to prevent the spinning of drive wheels on a slippery road surface. In particular, the TCS provides both traction control, which prevents excessive slipping of the drive wheels on a road when accelerating or starting from a stopped state to thereby improve acceleration performance, and trace control, which maintains the vehicle in a desired cornering radius such that cornering performance is enhanced. Such capabilities are typically performed by the TCS by controlling drive power transmitted to the drive wheels from the engine. Accordingly, TCSs act both as a vehicle performance enhancer and a safety device.
The different types of TCSs include a system which controls brake pressure; a system which varies ignition timing and fuel injection amounts, thereby controlling engine output; a system which controls the throttle valve to control engine output; and a system which uses a mixture of two or more of these methods. The system which controls the throttle valve to control engine output is again classified into two types: a main throttle actuator (MTA) system and a twin throttle body system (TTS).
When utilizing the TTS, both a main throttle valve and a TCS auxiliary throttle valve are mounted on the vehicle. The TCS auxiliary throttle valve is linked with the main throttle valve, then is electrically driven when slipping of the drive wheels on the road surface occurs. By electrically driving the auxiliary throttle valve, the problem of reaction time delays experienced with conventional throttle valves is overcome.
However, the application of the TTS necessitates complicated changes in the wiring and engine. Also, a TCS algorithm must be added to an engine control unit when using either the TTS or the method in which fuel injection is controlled. Finally, in the conventional TCS, information related to the shifting of gears is received from a TCU so that engine output can be controlled. As a result, when applying the TCS to a vehicle equipped with a manual transmission, since no means to supply such information to the TCS is available, a separate algorithm which calculates gearshift data based on vehicle driving states must be used. This leads to compatibility problems with regard to the algorithm since each vehicle is different.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a slip control method for a traction control system used in a vehicle in which, without the use of separate drive data, an opening degree of a main throttle valve is controlled when drive wheel slippage is detected such that engine output is controlled, thereby preventing the slipping of the drive wheels, and ultimately improving vehicle performance and enhancing vehicle safety.
To achieve the above object, the present invention provides a slip control method for a TCS used in vehicles. The method comprises the steps of generating variables for controlling engine output according to speeds of each wheel after a drive state is determined using wheel speeds, a throttle valve opening, and an accelerator pedal position; determining whether the TCS requires activation or de-activation according to the generated variables and the determined drive state; generating a first control variable for traction control after performing initial traction control if it is determined that immediately previous traction control was not performed, and directly generating a second control variable for traction control if it is determined that immediately previous traction control was performed, the first control variable and the second control variable being generated if it is determined in the previous step that the TCS requires activation; and controlling drive wheel speed through engine output control, the engine output control being performed by varying the throttle valve opening according to either the first control variable or the second control variable.
According to a feature of the present invention, in the step of generating variables for controlling engine output according to speeds of each wheel, a vehicle speed variable is generated as an average speed of rear wheels, a drive wheel average speed variable is generated as an average speed of front wheels (drive wheels), a slip rate variable is generated by subtracting the vehicle speed from a wheel speed and dividing the result by the wheel speed, and the drive wheel which is rotating faster becomes the object for control.
According to another feature of the present invention, in the step of determining whether the TCS requires activation or de-activation, one of the following four conditions must be satisfied to determine that the TCS requires activation: (a) when the vehicle is started from a stopped position, whether a slip ratio of drive wheels is greater than a predetermined first slip ratio, and a vehicle speed is above a predetermined first vehicle speed; (b) when the vehicle is in a normal state of driving, whether an opening degree of a throttle valve is less than that corresponding to a position of an accelerator pedal, and the TCS was previously activated; (c) when the vehicle is in a normal state of driving, whether the TCS was previously in an OFF state, the vehicle speed is greater than a predetermined second vehicle speed, and the slip ratio of the drive wheels is above a predetermined second slip ratio; or (d) when the vehicle is driving on a road surface with an extremely low level of traction, whether the vehicle speed has not reached a predetermined third vehicle speed and an average speed of the front wheels is above a predetermined value; and one of the following three conditions must be satisfied to determine that the TCS requires de-activation: (a) the driver controls a TCS switch to an OFF position; (b) the driver manipulates a brake pedal; or (c) the vehicle speed has reached a predetermined speed.
According to yet another feature of the present invention, the initial traction control is performed using only a vehicle speed in a vehicle with a manual transmission since information related to the transmission of power by a clutch and information of a present state of the transmission can not be known, and in the initial traction control, information to determine road conditions is obtained and a control variable for subsequent TCS control through control of drive wheel speed is generated.
According to still yet another feature of the present invention, the initial traction control comprises the step of controlling the throttle valve opening to a minimal degree according to the vehicle speed to artificially remove excessive slipping at an initial state; and maintaining the throttle valve opening at a predetermined opening degree to remove remaining excessive slipping or prevent the closing of the throttle valve in excess of what is required.
According to still yet another feature of the present invention, in the step of controlling the throttle valve opening to a minimal degree according to the vehicle speed, a time for controlling the throttle valve to the minimal degree from an initial state is determined by TCS ON conditions.
According to still yet another feature of the present invention, in the step of maintaining the throttle valve opening at the predetermined opening degree, if excessive slipping is not reduced below an expected value, the throttle valve is further closed a predetermined amount, and if wheel speed is overly reduced, the throttle valve is opened a predetermined amount.
According to still yet another feature of the present invention, the step of generating the first control variable and the second control variable for traction control further comprises the steps of determining a road condition by monitoring the drive wheels, the road condition being determined by the fastest-rotating drive wheel; determining a target slip rate for the traction control of the drive wheels according to the determined road condition; and determining a gain corresponding to the target slip rate for use in the traction control, the traction control being performed by controlling a rotating speed of the drive wheels according to the gain.
According to still yet another feature of the present invention, in the step of determining the road condition, in the case where the throttle valve is closed according to a control pattern, vehicle speed conditions are compared to determine whether wheel speeds reduce abruptly or smoothly such that road conditions of a high-traction road, slippery road surface (e.g., snowy and icy road conditions), low-traction road, etc. are determined.
According to still yet another feature of the present invention, in the step of controlling the drive wheel speed according to the first control variable and the second control variable, the throttle valve opening for controlling engine output is determined through proportional integration control such that a rotation of the drive wheels corresponds to a target vehicle speed, the proportional integration control utilizing the first control variable and the second control variable.
According to still yet another feature of the present invention, the target vehicle speed is determined from a target slip rate, the target slip rate being determined according to a determined road condition.
According to still yet another feature of the present invention, a control error in the proportional integration control is obtained from a difference between the target vehicle speed and a rotational speed of the faster drive wheel.